Welded pipe structure of high strength low alloy steels

ABSTRACT

A steel composition having particular applicability to the manufacture of high-strength, low-alloy line pipe comprises 0.10 to 0.20 percent carbon, 0.85 to 1.25 percent manganese, 0.10 percent maximum phosphorus, 0.05 percent maximum sulfur, silicon in an amount not adversely affecting steel properties, 0.02 to 0.05 percent columbium, 0.10 percent maximum vanadium, an inclusion shape-control agent selected from the group consisting of zirconium, a rare earth or mischmetal, the balance iron.

O United States Patent 1151 3,661,537

Aronson et al. 1 May 9, 1972 54] WELDED PIPE STRUCTURE OF HIGH 2,840,872 7/1958 Bidner ..75/129 x STRENGTH LOW ALLOY STEELS 2,861,908 11/1958 Mickelson 148/36 3,207,637 9/1965 Matuschka .....148/12.4 [72] lnventors: Arthur H. Aronson, Pittsburgh; Edward J. 3 231,712 V1966 15/123 R X 91 if i 3,544,393 12 1970 Zanetti ..148/12 samways 3,562,028 2/1971 Heitmann ..75/123 N x sburgh, all of Pa. [73] Assignee: Jones 8: Laughlin Steel Corporation, Pitt- FOREIGN PATENTS OR APPLICATIONS Sburgh, 1,120,588 7/1968 Great Britain ..75 123 E [22] Filed: July 16, 1969 Primary Examiner-L. Dewayne Rutledge PP- N05 8421285 Assistant Examiner-J. E. Legru Attorney-T. A. Zalenski and G. R. Harris [52] U.S. CI ..29/l91, 29/196], 75/123 E,

75/123 G, 75/123 11, 75 123 J ABSTRACT [51] Int.Cl ..B2ld39/02 A Stee com position having particular applicability to the Fleld of Search R, 123 E, H, l23 G, manufacture f higkbstrength y li comprises 75,123 148/121 29/191 196'l 0.10 to 0.20 percent carbon, 0.85 to 1.25 percent manganese, 0.10 percent maximum phosphorus, 0.05 percent maximum [56] References Cned sulfur, silicon in an amount not adversely affecting steel pro- UNn-ED STATES PATENTS perties, 002m 005 percent columbium, 0.10 percent maximum vanadium, an 1nclus1on shape-control agent selected 5 1 8/ 1951 from the group consisting of zirconium, a rare earth or 21810318 10/1957 mischmetal,the balance iron. 3,097,294 7/1963 3,303,060 2/1967 Shimizu ..l48/12.1 4 Claims, 1 Drawing Figure vi 0 5 A 1: J u.

TEMPERA TURE.

TEMPERA TURE,

INVENTORS ARTHUR H. ARONSON EDWARD J. LICHY NORMAN L. SAMWAYS CLIFFORD A. GUESS ATTORNEY WELDED PIPE STRUCTURE OF HIGH STRENGTH LOW ALLOY STEELS The present invention relates to high-strength low-alloy steels having improved properties. The steels are particularly useful in the manufacture of electric-resistance welded line pipe.

Non-metallic inclusions in a high-strength low-alloy steel reduce the steels resistance to ductile fracture and impair its forming properties. Deterioration of these properties increases with increasing numbers of inclusions and increasing inclusion elongation. We have developed high strength lowalloy steels having an inclusion type and morphology far less deleterious to toughness and formability. The steels of the invention have particular applicability to the manufacture of welded line pipe and result in pipe of improved flattenabilty and toughness.

The desired inclusion characteristics are achieved by controlling overall steel chemistry and deoxidation practice and, most importantly, by the use of an inclusion shape-control agent comprising zirconium, a rare earth, e.g., cerium, lanthanum, praseodymium, neodymium, yttrium, and scandium, or mischmetal which, of course, is a mixture of rare earths. The use of an inclusion shape-control agent results in the formation of spherically shaped inclusions, particularly sulfide inclusions, which are not plastic at hot-rolling temperatures and consequently do not become elongated but retain their spherical shape in the finished steel.

An object of the present invention is to provide steels of improved toughness and ductility. Another object of the invention is to provide welded line pipe characterized by improved flattenability and weld toughness.

These and other objects and advantages of the present invention will become apparent from the following detailed disclosure with reference to the FIGURE of the drawing which is a graphical representation of the improved impact properties possessed by the steels of the present invention.

The steels of the present invention are fully aluminum-killed and have the following chemistry in weight percents: carbon, 0.10 to 0.20 percent; manganese, 0.85 to 1.25 percent; phosphorus, 0.10 percent maximum; sulfur, 0.05 percent maximum; silicon, in amounts not adversely affecting steel properties; columbium, 0.02 to 0.05 percent; vanadium, 0.10 percent maximum; and an inclusion shape-control agent comprising 0.04 to 0.20 percent zirconium, a minimum of about 0.02 percent of a rare earth or mischmetal; and balance iron. To insure good recovery, the inclusion shape-control agent preferably is added to the steel in the ingot mold or in the ladle after the steel has been killed.

The requisite high strength is imparted to the steel by hot rolling it in a manner to achieve a finishing temperature within the range of l,550 to 1,650 F, followed by in-line cooling at a rate of to 135 F per second to a coiling or piling temperature within the range of 975 to 1,125 F. As indicated above, the spherically shaped inclusions formed through the use of the inclusion shape-control agent are not plastic at hot-rolling temperatures and retain their desired spherical form in the finished product. In its preferred application, the manufacture of welded line pipe, the steel is hot-rolled into skelp, formed, and electric-resistance welded.

The superior impact properties possessed by welded line pipe manufactured according to the present invention is shown in the FIGURE of the drawing. The data on which the FIGURE is based were obtained from transverse one-half size Charpy V-notch specimens taken from 12% inch OD. electric-resistance-welded line pipe. For line pipe manufactured from a semi-killed columbium-vanadium high-strength lowalloy steel not containing an inclusion control agent, all impact data fell within the cross-sectioned area of the figure. This type of steel has been used quite extensively in the manufacture of line pipe. All of the individual data points plotted on the figure were obtained from specimens having chemistries within the ranges of the steels of the present invention, as set out above, and employing zirconium as the inclusion shapecontrol agent. The dashed curve drawn through these oints is a conservative estimate of the transition curve and 11 ustrates that, typically, the steels of the present invention result in pipe with transverse l2 ft.-lb. transition temperatures of minus 30 F.

Improved flattening behavior of welded pipe manufactured from the steels of the present invention is shown in the following table:

high-strength low-alloy steel of the type referred to above. Welded pipe runs 2, 3 and 4 comprised fully killed steels having compositions falling within the ranges of steels of the invention, as set out above, and containing zirconium as an inclusion shape-control agent. The tests reported in the table were carried out as described in paragraphs 4.14 through 4.16 of API Std. SLX, 16th edition, April 1969.

Control of inclusion shape, which is primarily responsible for the improved properties possessed by the steels of the present invention, is also obtained through the use of 0.01 to 0.10 percent of a rare earth or mixture of rare earths such as mischmetal.

We claim:

1. A welded pipe structure formed of a fully killed steel having a composition consisting essentially of 0.10 to 0.20 percent carbon, 0.85 to 1.25 percent manganese, 0.10 percent maximum phosphorus, 0.05 percent maximum sulfur, silicon in an amount not adversely affecting steel properties, 0.02 to 0.05 percent columbium, 0.10 percent maximum vanadium, an inclusion shape-control agent selected from the group consisting of 0.04 to 0.20 percent zirconium, 0.01 to 0.10 percent of a rare earth and 0.01 to 0.10 percent mischmetal, balance iron.

2. A welded pipe structure as defined in claim 1 wherein the inclusion shape-control agent comprises 0.04 to 0.20 percent zirconium.

3. A welded pipe structure as defined in claim 1 wherein the inclusion shape-control agent comprises 0.01 to 0.10 percent of a rare earth.

4. A welded pipe structure as defined in claim 1 wherein the inclusion shape-control agent comprises 0.01 to 0.10 percent mischmetal. 

2. A welded pipe structure as defined in claim 1 wherein the inclusion shape-control agent comprises 0.04 to 0.20 percent zirconium.
 3. A welded pipe structure as defined in claim 1 wherein the inclusion shape-control agent comprises 0.01 to 0.10 percent of a rare earth.
 4. A welded pipe structure as defined in claim 1 wherein the inclusion shape-control agent comprises 0.01 to 0.10 percent mischmetal. 